The present invention concerns vehicle tire safety supports that are mounted inside the tires, on their rims, in order to carry the weight in case of tire failure. In particular, it concerns the connection between those safety supports and the rims on which they are mounted.
The main function of the safety supports is to carry the weight in case of severe loss of inflation pressure of the tire. When tires are inflated normally, the safety supports should interfere with the dynamic properties of the tires as little as possible. In particular, they should remain well centered around the rim in order to avoid any unbalance effect, whatever the temperature of the support and the traveling speed of the vehicle. They should also be capable of being mounted on the rims of vehicle wheels and demounted easily.
U.S. Pat. No. 5,690,762 relates to a safety support made of an elastic material designed to be mounted on a well-base rim of an ordinary passenger vehicle. This support contains a body and a base designed to come in contact with the rim. The support further includes annular reinforcements circumferentially oriented and appreciably inextensible, the radius of which is slightly greater than the radius of the flange of the rim for which the support is provided. The base consists of two annular zones, whose inner radius in free state is less than that of the part of the rim on which they must bear; the compression of these annular zones therefore ensures good centering of the support on the rim. The function of the annular reinforcements is, notably, to prevent the annular zones from stretching, by reason of high-speed centrifugal forces, until losing contact with the rim.
When a safety support is designed to equip a rim in two parts or a rim possessing a bearing for a support, the radius of which is greater than that of one of the rim flanges, as shown in FIG. 1, the safety support is mounted by insertion of the support on the corresponding rim bearing. One can refer to U.S. Pat. No. 5,836,366 which describes a method of mounting an assembly made up of a tire and tread support on such a wheel rim bearing. It is important for the support to be well centered on the rim bearing while maintaining easy mounting and demounting, as well as satisfactory endurance.
On the other hand, when annular reinforcements are necessary to withstand centrifugal forces, the annular reinforcements can be placed in the base. This is the case with the support disclosed by application EP 0,796,747 A1. Such a position of the annular reinforcements facilitates the manufacture of the support.
For such a support, taking into account the manufacturing tolerances of the rim and support, it is no longer possible to use radially inner annular zones, the compression of which ensures good centering on the rim, whatever the speed, while ensuring easy mounting and demounting.
xe2x80x9cEquatorial planexe2x80x9d of a safety support is understood to be any plane perpendicular to the axis of rotation of the support and xe2x80x9cmid-equatorial planexe2x80x9d is understood to be the equatorial plane placed in the middle of the support.
The xe2x80x9caxial planexe2x80x9d of a support or wheel is understood to be any plane passing through the axis of rotation of the support or wheel.
According to a first aspect, the object of the invention is a safety support designed to be inserted by a relative translation operation on a wheel rim bearing, said support having an axially front face and an axially back face and containing a base intended to fit around said bearing as well as a body connected to said base, said bearing having an engagement edge and said translation operation consisting of moving the engagement edge of the rim bearing of said axially front face of the support toward said axially back face, characterized in that the radially lower surface of the support presents a plurality of circumferentially distributed centering protuberances, each of said centering protuberances possessing in section through an axial plane at least one portion of a radially inner profile, whose distance from the axis of the support gradually diminishes in the axial direction between a value exceeding the radius of the engagement edge of the rim bearing on the front side of the support and a value less than that radius toward the back side of the support, in order to permit a friction engagement between the rim and the support.
The presence of the centering protuberances makes it possible to bring about their compression with extension of the support upon its insertion around the rim bearing. This ensures good centering of the support in relation to the rim. The particular shape of said protuberances further makes it possible to transform them into actual guides of the support, which markedly facilitates mounting on the bearing, notably, in the zone of the support where, by reason of the thickness of the protuberance, mounting results in a compression of the latter.
According to a second aspect, the invention concerns a similar safety support in which each of said centering protuberances possesses in section through an axial plane at least one radially inner profile portion, whose distance from the axis of the support gradually diminishes in the axial direction between a value exceeding the radius of the engagement edge of the rim bearing on the back side of the support and a value less than that radius toward the front side of the support.
This second characteristic is particularly advantageous. It markedly facilitates demounting of the support by preventing the edges of the protuberances from being stopped against any part of the rim that the protuberance must pass.
The invention also concerns a similar safety support designed to be inserted by a relative translation operation around a rim bearing, said support containing a base intended to fit around said bearing, as well as a body connected to said base, said body containing suitable zones for defining cavities separating the base and the radially outer part of the support and distributed around the support, characterized in that the radially inner surface of said base of the support presents a plurality of circumferentially distributed centering protuberances, and in that at least some of said protuberances are radially arranged internally opposite corresponding cavities in said body.
This arrangement has the advantage of limiting the variations of radial stiffness of the support as a function of the azimuth and, consequently, upon running on support, of diminishing the variations of forces sustained by the support, as well as the vibrations produced by the protuberances. This results in an appreciable improvement of endurance of these supports in operation.
According to an additional aspect, an object of the invention is a safety support of the general type in which the base contains a zone of resistance appreciably inextensible circumferentially, but flexible, the radially inner radius of which is slighter greater than the radius of the rim support bearing, as well as means for centering the support relative to the rim. This support is characterized in that the centering means consist of a plurality of circumferentially distributed protuberances radially arranged internally relative to the zone of resistance of the base and the radially inner walls of which are inscribed in free state on a radius less than the radius of the rim support bearing.
The protuberances radially arranged internally relative to the zone of resistance generate, by their radial compression, tightening stresses on mounting of the support, but also have the advantage of making possible a polygon formation of the zone of resistance that is flexible and very slightly extensible. Said polygon formation makes it possible to absorb some variation of radius of the rim support bearing or of the zone of resistance and thus ensure easy mounting of the support, while maintaining excellent resistance to centrifugal force.
The protuberances are preferably arranged symmetrically in relation to the axis of rotation of the support.
The axial width of the protuberances can range between 10 and 50% of the axial width of the base of the support.
According to a preferred embodiment, the protuberances are arranged axially on the side of the axially back face of the support.
This makes it possible to facilitate mounting by not requiring an extension of the base or, as the case may be, a polygon formation of the zone of resistance of the base at the end of mounting of the support on the rim.
The protuberances can present axially, on the side of the axially back face of the support and/or on the side of the axially front face of the support, a lateral face whose average inclination relative to the axis of rotation of the support ranges between 15 and 55 degrees. Said lateral face facilitates demounting of the support by enabling the side of the support first leaving the rim bearing not to be stopped against the outer flange of the rim.
The straight section of the protuberances in an axial plane can be trapezoid-shaped. Preferably, xcex1 being the half-angle in the center separating two adjacent protuberances, and R being the radius of the support bearing 4 of the rim 2, the height h of a protuberance satisfies the following relation:   h  ≤      R    ⁡          (                        1                      cos            ⁢                          xe2x80x83                        ⁢            α                          -        1            )      
When that relation is satisfied, on polygon formation of the base around the rim support bearing, there is always a zone of contact between the base and the support bearing between the two adjacent protuberances. The limiting value of the height of the protuberances corresponds to the maximum efficiency of the protuberances.
The radial height of the protuberances ranges between 2 and 10 mm and preferably between 3 and 5 mm.
The radial height of the protuberances should not be too elevated, in order not to entail, upon running on the support, the vibrations which might be detrimental to the endurance of the support. However, if these vibrations are perceptible to the driver, that can be an advantage in order to indicate that the running conditions no longer necessitate a reduction of traveling speed. A radial height in the order of 3 to 5 mm appears to be a good compromise. The effectiveness of the take-up of play linked to the polygon formation of the zone of resistance, for a given radial height of protuberances, directly depends on their number. For a radial height of 3 to 5 mm, a number of protuberances ranging between 3 and 15 makes it possible to fill all the necessary base diameter variations due to production process.
When the base of the support includes a plurality of extensions stretching axially away from the side opposite to the first mounting side, the protuberances can be arranged at the same azimuths as those extensions.
The radially inner surface of said base can also at least contain, between two circumferential zones of given radius, a circumferential zone of greater radius.
This central recess of the base of the bearing facilitates its mounting and demounting by limiting friction against the rim support bearing.
The protuberances can be distributed in two assemblies axially and circumferentially offset from each other. This has the advantage, upon running on the support, of inducing a movement comparable to a camber movement. The vibrations resulting therefrom can be either directly felt by the driver of the vehicle or detected by an appropriate device.
The invention also concerns a wheel assembly containing a rim and a safety support, said support being designed to be inserted by a relative translation operation around a bearing of said rim, having an axially front face and an axially back face and containing a base intended to fit around said bearing as well as a body connected to said base, said bearing having an engagement edge and said translation operation consisting of moving the engagement edge of the rim bearing of said axially front face of the support to said axially back face, characterized in that said assembly contains a plurality of circumferentially distributed protuberances, compressed radially between the base of said support and said rim bearing in order to create an appropriate mechanical tightening between said support and said bearing and to ensure the centering of said support on said bearing.
This assembly can be such that the protuberances are arranged on the radially outer surface of the rim bearing. In that case it is advantageous for each of said centering protuberances to possess in section through an axial plane at least one radially outer profile portion whose distance from the axis of said rim gradually increases in the axial direction, going from the side of the engagement edge of said bearing to the opposite side, between a value less than the inner radius of the base of said support and a value exceeding that radius, in order to make possible a friction engagement between the rim and the base of the support.